Resonator for torsional vibration

ABSTRACT

A generally disc-shaped ferroelectric ceramic piece is provided with at least one recess inwardly extending from the peripheral surface and is poled along the azimuthal direction so as to adapt the piece to torsional vibration. A pair of electrodes are attached to the principal surfaces of the piece, respectively. During manufacture, a pair of electrodes for poling the piece are attached to the face of the piece provided by the recess and are removed after poling.

I I U- 2,928,069 3/1960 Petermann 310/9.6 X

3,020,424 2/1962 Bechmann 3l0/9.6 X

3,405,289 10/1968 Gikow 310/96 X 3.074.034 1/1963 Crownover BIO/9.6 X

OTHER PUBLICATIONS IBM Technical Disclosure Bulletin, Piezoelectric Transducer, by W. V. Vilkelis, Vol. 6, No. 8, Jan. 1964.

Primary Examiner-Mark O. Budd Att0meyNich0l M. Sandoe et al.

[57] ABSTRACT A generally disc-shaped ferroelectric ceramic piece is provided with at least one recess inwardly extending from the peripheral surface and is poled along the azimuthal direction so as to adapt the piece to torsional vibration. A pair of electrodes are attached to the principal surfaces of the piece, respectively. During manufacture, a pair of electrodes for poling the piece are attached to the face of the piece provided by the recess and are removed after poling.

11 Claims, 13 Drawing Figures Tsubouchi 1 RESONATOR FOR TORSIONAL VIBRATION [75] Inventor: Norio Tsubouchi, Tokyo, Japan [73] Assignee: Nippon Electric Company, Limited,

Minato-ku, Tokyo, Japan [22] Filed: Apr. 17, 1972 [21] Appl. No.: 244,401

[30] Foreign Application Priority Data Apr. 21, 1971 Japan 46/26231 [52] U.S. Cl 310/95, 310/9.6, 3l0/8.5, I 333/72 [51] Int. Cl H04r 17/00 [58] Field of Search 310/95, 9.6; 333/72, 71

[56] References Cited UNITED STATES PATENTS 3,396,327 8/1968 Nakazawa 310/94 X 3,284,727 11/1966 Carlson et a1 310/9.6 X

, Q1 xvi RESONATOR FOR TORSIONAL VIBRATION BACKGROUND OF THE INVENTION This invention relates to a ferroelectric or piezoelectric ceramic resonator to be put into torsional vibration and a method of making the same.

Piezoelectric ceramic resonators for the longitudinal vibration or thickness shear vibration have been used as the transducers in mechanical filters which are widely in use in telecommunication apparatus. With such ceramic resonators, it is possible to use the electrodes used to pole the ceramic pieces as the electrodes for excitation and vibration. This makes it possible to assemble a piezoelectric ceramic resonator and has provided a wider use thereof.

With the progress of the telecommunication technique, it is strongly desired to reduce the dimensions of the mechanical filters and to widen the band width thereof. It is, however, difficult to satisfy these requirements with conventional piezoelectric ceramic resonators. More particularly, a conventional piezoelectric ceramic resonator has poor electromechanical conversion efficiency and a high propagation speed of sonic waves. The poor electromechanical conversion efficiency makes it difficult to provide the filter with a wide band width. The high propagation speed makes it difficult to miniaturize the piezoelectric resonator.

Access has therefore been desired towards a piezoelectric ceramic resonator having excellent electromechanical conversion efficiency and a moderately slow propagation speed. This has drawn attention to piezoelectric ceramic resonators to be used in the torsional mode of vibration, which satisfies, in theory, the desires. It is, however, to be noted that the direction of the electric fields for poling must be varied from place to place, in the manner later explained with reference to one of the accompanying drawings, in order to manufacture a piezoelectric ceramic resonator to be put in the torsional mode of vibration. This imposes difficulties on the manner of furnishing the piezoelectric ceramic piece with the electrodes for poling. An attempt has therefore been made to remove the difficulties as will be described with reference to another of the accompanying drawings. The attempt, however, is still incapable of attaining the satisfactory poling and results in the survival of unpoled portions and in the consequent reduction of the piezoelectric activities.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a piezoelectric ceramic resonator of the shape with which it is easy to provide the electrodes for poling the piezoelectric ceramic piece so as to adapt the piece to the torsional mode of vibration.

Another object of this invention is to provide a piezoelectric ceramic resonator of the shape with which it is easy to miniaturize the resonator.

Still another object of this invention is to provide a piezoelectric ceramic resonator by which application to the piezoelectric ceramic piece of the electric field for poling will not leave unpoled portions in the piece.

Yet another object of this invention is to provide a piezoelectric ceramic resonator whichshows excellent piezoelectric activities.

A further object of this invention is to provide a method of making a piezoelectric ceramic resonator of any of the types described.

According to the instant invention there is provided a ceramic resonator comprising a ferroelectric ceramic piece of a generally disc shape having two parallel principal surfaces, a cylindrical peripheral surface joining said principal surfaces, and a pair of electrodes attached to said principal surfaces, respectively. The piece is poled along the paths between and substantially parallel to the principal surface so as to adapt said resonator to the torsional mode of vibration. The improvement comprises at least one recess inwardly extending from said peripheral surface into the body of said disc, the face of said piece provided by said recess being substantially perpendicular to said principal surfaces.

According to this invention there is also provided a method of making a ceramic resonator comprising the steps of forming a ferroelectric ceramic piece of a generally disc shape having two parallel principal surfaces and a cylindrical peripheral surface joining said principal surfaces, providing at least a pair of first electrodes to said piece, applying an electric field between said pair of said first electrodes to pole said piece and adapt said piece to the torsional mode of vibration whereby its principal surfaces move in opposite directions, removing said first electrodes, and then attaching a pair of second electrodes to said principal surfaces, respectively, characterized in that said piece is formed at least one recess inwardly extending from said peripheral surface into the body of said disc, the face of said piece provided by said recess being substantially perpendicular to said principal surfaces, and that said first electrodes are attached to said face of said piece provided by said recess so as to allow application of said electric field.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a piezoelectric ceramic piece which illustrates the principles of the pres ent invention;

FIG. 2 is a perspective view of a piezoelectric ceramic piece produced during the manufacture of a conventional piezoelectric ceramic resonator adapted to the torsional mode of vibration;

FIG. 3 is a perspective view of a first example of a piezoelectric ceramic piece for use in an embodiment of this invention;

FIG. 4 is a perspective view of an embodiment of this invention;

FIG. 5 is a perspective view of a second example of a piezoelectric ceramic piece;

FIG. 6 is a plan view of a third example of a piezoelectric ceramic piece;

FIG. 7 is a perspective view of a fourth example of a piezoelectric ceramic piece;

FIG. 8 is a perspective view of a fifth example of a piezoelectric ceramic piece;

FIG. 9 is a perspective view of a sixth example of a piezoelectric ceramic piece;

FIG. 10 is a perspective view of a seventh example of a piezoelectric ceramic piece;

FIG. 11 is a perspective view of an eighth example of a piezoelectric ceramic piece;

FIG. 12a is a plan view of a mechanical filter comprising an embodiment of this invention; and

FIG. 12b is an elevational view of the mechanical filter.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, it is necessary in order to provide a piezoelectric ceramic piece 20 adapted to the torsional mode of vibration to subject the piece 20 to an electric field 21 whose direction varies along the azimuth of the piece 20. It has, however, been impossible to realize this ideal distribution of the field 21.

Referring to FIG. 2, a conventional method of making a piezoelectric ceramic resonator adapted to the torsional mode of vibration comprises the steps of providing a piezoelectric ceramic piece 20 having a bore 22 at the center, providing a plurality of electrodes 23 on both principal surfaces of the piece 20 in the manner depicted in the drawing, and applying an electric field 21 between each pair of the neighbouring electrodes, such as 23, and 23 for poling the piece 20. This method not only leaves unpoled portions at the sections where the electrodes 23 are attached to the principal surfaces but also restricts the poled portions to the adjacencies of the principal surfaces. This further gives rise, on exciting the piezoelectric torsional vibration, to unwanted additional load and to the consequent reduction in the piezoelectric activities.

Referring to FIG. 3, a first example of the piezoelectric ceramic piece 20 of a generally disc shape for use in an embodiment of the instant invention has two substantially parallel principal surfaces and a substantially circular cylindrical peripheral surface joining the principal surfaces. The piece 20 further has a recess 26 extending inwardly from the peripheral surface into the body of the disc. The face 27 of the piece 20 provided by the recess 26 is substantially perpendicular to the principal surfaces. The recess 26 is generally V-shaped so that the face 27 is divided into two face portions 27, and 27 each forming a selected angle with a radius of the disc. During manufacture, a pair of electrodes 23, and 23 are attached to the face portions 27, and 27 respectively. An electric potential is applied between the electrodes 23, and 23 which produces an electric field 21 in the piece 20 varying along the azimuthal direction for poling the piece 20 in the known manner so as to adapt the piece 20 to the torsional mode of vibration. Thus, the piece 20 is poled along paths between and substantially parallel to its principal surfaces. Subsequently, the electrodes 23, and 23 are removed.

Referring to FIG. 4, an embodiment of this invention comprises a piezoelectric ceramic piece 20 manufactured either in the manner described above with reference to FIG. 1 or in the manner to be later described with reference to any one of FIGS. through 1 l. A pair of metal pieces 31 and 32 are attached to the principal surfaces of the piece 20, respectively, to complete a resonator of the Langevin type. These metal pieces 31 and 32 may be fixed to the piece by means of an electroconductive binding agent and used as the electrodes for exciting the desired torsional vibration.

Referring to FIG. 5, a second example of the piezoelectric ceramic piece 20 has a shape similar to that of the first example but has a generally cylindrical bore 22 substantially at the center of the piece 20, in substantially concentric relation to the peripheral surface and in communicating relation to the recess 26. The face 27 of the piece 20 is thus divided into two face portions 27, and 27,. The electrodes 23, and 23, are attached preferably to the whole face portions 27, and 27,, re-

spectively. Also preferably, the face portions 27, and 27 are substantially planes respectively, and the largest distance d between such two face portions 27, and 27 is not greater than 0.9 times the diameter of the peripheral surface. The smallest distance between these two face portions 27, and 27 may be zero. In other words, the central bore 22 need not necessarily be in communicating relation to the recess 26. It is, however, to be noted that the communicating relation facilitates the application and removal of the electrodes 23, and 23 to and from the ceramic piece 20. Furthermore, the central bore 22 and the recess 26 may be of configuration such that the bore 22 has the shape of a semicircle and the recess 26 has the shape of a triangle that has a base coincident with the circle-dividing diameter and is truncated by the circle of the peripheral surface.

Referring further to FIG. 5, it has been confirmed by a series of experiments carried out with piezoelectric ceramic resonators, each comprising a piezoelectric ceramic piece 20 described above with reference to FIG. 5, that the best results are obtained when the diameter of the central bore 22 is within a range between 0.2 through 0.9 times that of the peripheral surface.

Referring to FIG. 6, a third example of the piezoelectric ceramic piece 20 is a variation of the second example and has a central bore 22 and a communicating recess 26 bounded by a pair of substantially parallel plane face portions 27, and 27 The electrodes 23, and 23 for poling are attached to the face portions 27, and 27 and subsequently removed after poling. The piece is thus poled along paths that are arcuate and concentric with respect to the peripheral cylindrical surface of the disc. The diameters a and b of the peripheral surface and the bore 22 and the distance d of the face portions 27, and 27 will be referred to later.

Referring to FIG. 7, a fourth example of the piezoelectric ceramic piece 20 has three recesses 27A, 27B, and 27C. The faces 27A, 27B, and 27C provided by the respective recesses 26A, 26B, and 26C are substantially perpendicular to the respective radii 41, 42, and 43 of the disc which substantially trisect the disc. A pair of electrodes 23, and 23 is attached to one of the faces 27A at a portion offset to left in the drawing and to an adjacent face 278 at a portion reversely offset to right in the drawing respectively. In this manner, three pairs of electrodes 23 are attached to the piece 20 for production of the electric fields 21 for poling the piece 20 in the desired manner along paths that are cordal with respect to the cylinder defined by the peripheral surface of the disc.

Referring to FIG. 8, a fifth example of the piezoelectric ceramic piece 20 is similar to the fourth example but has a central bore 22.

Referring to FIG. 9, a sixth example of the piezoelectric ceramic piece 20 is similar to the fifth example but has a further recess 46 inwardly extending from each of the faces 27A, 27B, and 27C into the body of the disc, starting in the vicinity ofa line which is perpendicular t0 the principal surfaces and substantially bisects the area of one face 27A, 278, or 27C. The further recesses 46 serve to define the offset portions of the faces 27A, 27B, and 27C, respectively.

Referring to FIG. 10, a seventh example of the piezoelectric ceramic piece 20 has four recesses 26A, 26B, 26C, and 26D. The faces 27A, 27B, 27C, and 27D provided by the recesses 26A, 26B, 26C, and 26D, respectively, are substantially perpendicular to the respective radii 51, 52, 53, and 54 of the disc which are in substantially quadrature relation to one another. Four pairs of electrodes 23 are attached to the piece 20 for poling the piece 20 in a manner similar to the electrodes 23 of the fourth and the fifth examples.

Referring to FIG. 1 1, an eighth example of the piezoelectric ceramic piece 20 is similar to the seventh example but has a further recess 46 inwardly extending from each of the faces 27A, 27B, 27C, and 27D like the sixth example.

EXAMPLES Lead zirconate-titanate ceramic pieces 20 of disc shape, 5 mm in diameter and 1 mm in thickness, and of annular disc shape having a central bore 22 of 1.23 mm in diameter, were provided. The electromechanical coupling coefficient K, under the radial mode of vibration was 42 percent, and the mechanical quality factor Q, under the same condition was 1,500. Each piece 20 was provided with at least one recess 26 in the manner illustrated with reference to FIG. 3 and FIGS. 5 through 1 1. As is known in the art of the piezoelectric ceramic materials, the piece 20 may be made directly into either the disc shape or the annular shape having at least one recess 26. At least one pair of first, silver electrodes 23 for poling the piece 20 was attached to the face or faces 27 provided by the (at least one) recess 26. Poling was carried out under a D.C. electric field 21 between 2 and 3 kV/mm at a temperature of 100C for 30 minutes. Subsequently, the first electrodes 23 were removed. So prepared piece 20 was placed between a pair of second electrodes 31 and 32 for exciting the vibration. The second electrodes 31 and 32 or the metal pieces 31 and 32 may be 5 mm in diameter and 7 mm in length and made of an ironnickel-chromium alloy called Elinvar.

TABLE 1 Mech. Shape of Resonant Capacitance Quality Piece 20 Freq. F Ratio r Factor 0,.

(kHz) FIG. 77.87 18 570 FIG. 7 72.50 29 220 FIG. 9 67.51 19 170 FIG. 11 72.66 32 230 Table 1 shows the results obtained for thus manufactured piezoelectric ceramic resonators for the resonant frequencies F the capacitance ratios r, and the mechanical quality factors Qm. From Table 1, it is obvious that the piecoelectric ceramic resonators have moderately low resonant frequencies F which is due to the fact that the torsional vibration has a relatively low propagation speed for sonic waves. It is also clear that the capacitance ratios r are sufficiently small and consequently that the piezoelectric activities are much improved. Furthermore, it is apparent that the piezoelectric ceramic resonator including the piezoelectric ceramic piece 20 of the shape depicted in FIG. 5 exhibits a remarkably high mechanical quality factor 0,

TABLE 2 Mech. Resonant Capacitance Quality 1; b Freq. F Ratio r- Factor 0,

(kHz) 4 2 106.72 840 5 2 108.20 24 870 7 2 108.47 22 810 7 3 108.02 26 1050 7 4 105.23 23 830 Of a piezoelectric ceramic materiai whose electromechanical coupling coefficient K, and mechanical quality factor Q, in the radial mode were 64 percent and 900, respectively, piezoelectric ceramic pieces 20 were made into the configuration shown in FIG. 6. Table 2 shows the resonant frequencies F the capacitance ratios r, and the mechanical quality factors 0,, for the torsional vibration. The pieces 20 were 1 mm thick. The distance d between the parallel plane surfaces was 1.2 mm. Examples of the diameter of the piece a and the bore b are given in Table 2. The lengths of a pair of Elinvar pieces 31 and 32 were 6.4 mm and 4.0 mm, respectively.

Referring to FIGS. 12a and 12b, a mechanical filter includes a pair of transducers 61, each having the piezoelectric ceramic piece 20, and a plurality of metal pieces 62. The transducers 61 and the metal pieces 62 are welded to a pair of supporting rods 63 and to several coupling rods 64.

It will be obvious to those skilled in the art that the embodiment described above is meant to be merely exemplary and that the specific structure of the apparatus and steps of the method are susceptible of modification and variation without departing from the spirit and scope of the invention. Therefore, the invention is not deemed to be limited except as defined by the appended claims.

What is claimed is:

l. A ceramic resonator comprising a ferro-electric ceramic piece that is generally disc shaped having two parallel principal surfaces, a cylindrical peripheral surface joining said principal surfaces, and a pair of electrodes attached to said principal surfaces, respectively, said piece being poled along paths between and substantially parallel to said principal surfaces so as to adapt said resonator to the torsional mode of vibration with its principal surfaces moving in opposite directions, wherein the improvement comprises at least one recess extending inwardly from the circle defined by said peripheral surface, the face of said piece formed by said recess being substantially perpendicular to said principal surfaces.

2. A resonator as set forth in claim 1, wherein there is only one recess and said face of said piece provided by said recess comprises two face portions, each portion forming a plane, said paths along which said piece is poled being arcuate and concentric with said peripheral surface. I

3. A resonator as set forth in claim I, wherein the greatest distance between said two face portions is not more than 0.9 times the diameter of said peripheral surface.

4. A resonator as set forth in claim 2, wherein said two face portions form a pair of substantially parallel planes, the distance between said planes, and the diameter of the piece being in the proportions 1.2, 2.0 and not more than 7.0, respectively.

5. A resonator as set forth in claim 1, wherein said recesses are three in number and each face of said piece which forms a recess is substantially perpendicular to one of three radii of said disc, said three radii trisecting said disc and said paths along which said piece is poled being cordal with respect to the cylinder defined by said peripheral surface.

6. A resonator as set forth in claim 5, wherein a further recess extends inwardly from each of said faces of 7 said piece starting in the vicinity of a line which is perpendicular to said principal surfaces and which substantially bisects the area of one of said faces.

7. A resonator as set forth in claim 1, wherein said recesses are four in number and said faces of said piece formed by the respective recesses are substantially perpendicular to four radii of said disc which are in quadrature relation to one another.

8. A resonator as set forth in claim 7, wherein a further recess extends inwardly from each of said four faces of said piece starting in the vicinity of a line which is perpendicular to a principal surface and which substantially bisects the area of one of said faces.

9. The resonator as set forth in claim 2, wherein each face portion forms an angle of 0 to with an intersecting radius of said disc.

10. The resonator as set forth in claim 1, further comprising a substantially cylindrical bore centrally disposed in said disc. said recess extending into said bore.

11. A resonator as set forth in claim 10, wherein the diameter of said bore is within a range between 0.2 and 0.9 times the diameter of said peripheral surface. 

1. A ceramic resonator comprising a ferro-electric ceramic piece that is generally disc shaped having two parallel principal surfaces, a cylindrical peripheral surface joining said principal surfaces, and a pair of electrodes attached to said principal surfaces, respectively, said piece being poled along paths between and substantially parallel to said principal surfaces so as to adapt said resonator to the torsional mode of vibration with its principal surfaces moving in opposite directions, wherein the improvement comprises at least one recess extending inwardly from the circle defined by said peripheral surface, the face of said piece formed by said recess being substantially perpendicular to said principal surfaces.
 2. A resonator as set forth in claim 1, wherein there is only one recess and said face of said piece provided by said recess comprises two face portions, each portion forming a plane, said paths along which said piece is poled being arcuate and concentric with said peripheral surface.
 3. A resonator as set forth in claim 1, wherein the greatest distance between said two face portions is not more than 0.9 times the diameter of said peripheral surface.
 4. A resonator as set forth in claim 2, wherein said two face portions form a pair of substantially parallel planes, the distance between said planes, and the diameter of the piece being in the proportions 1.2, 2.0 and not more than 7.0, respectively.
 5. A resonator as set forth in claim 1, wherein said recesses are three in number and each face of said piece which forms a recess is substantially perpendicular to one of three radii of said disc, said three radii trisecting said disc and said paths along which said piece is poled being cordal with respect to the cylinder defined by said peripheral surface.
 6. A resonator as set forth in claim 5, wherein a further recess extends inwardly from each of said faces of said piece starting in the vicinity of a line which is perpendicular to said principal surfaces and which substantially bisects the area of one of said faces.
 7. A resonator as set forth in claim 1, wherein said recesses are four in number and said faces of said piece formed by the respective recesses are substantially perpendicular to four radii of said disc which are in quadrature relation to one another.
 8. A resonator as set forth in claim 7, wherein a further recess extends inwardly from each of said four faces of said piece starting in the vicinity of a line which is perpendicular to a principal surface and which substantially bisects the area of one of said faces.
 9. The resonator as set forth in claim 2, wherein each face portion forms an angle of 0* to 90* with an intersecting radius of said disc.
 10. The resonator as set forth in claim 1, further comprising a substantially cylindrical bore centrally disposed in said disc, said recess extending into said bore.
 11. A resonator as set forth in claim 10, wherein the diameter of said bore is within a range between 0.2 and 0.9 times the diameter of said peripheral surface. 